Electric power conversion system

Abstract

An electronic control unit of an electric power conversion system is configured to, when voltages of first and second batteries are stepped up in parallel and a temperature of a common switching element exceeds a threshold temperature, execute on time change control such that following conditions i) and ii) are satisfied: i) a trailing edge of one of the first and second PWM signals and a leading edge of the other one of the first and the second PWM signals connect with each other; and ii) the sum of the on time of the first and second PWM signals in a single PWM control period falls within a range from the single PWM control period to an allowable period. The electronic control unit is configured to change an on time of at least one of the first and second PWM signal in the on time change control.

What is claimed is: 
     
       1. An electric power conversion system comprising:
 a first battery; 
 a second battery; 
 a voltage converter including a plurality of switching elements, the voltage converter being configured to bidirectionally step up and step down voltage between the first battery and an output line and between the second battery and the output line by turning on or off the plurality of switching elements in accordance with PWM signals, 
 in parallel step-up operation in which a voltage of the first battery and a voltage of the second battery are stepped up in parallel with each other, the voltage converter being configured to step up the voltage of the first battery by using a first step-up circuit and output a stepped-up voltage to the output line, and step up the voltage of the second battery by using a second step-up circuit and output the stepped-up voltage to the output line, and 
 the plurality of switching elements including a common switching element that is supplied with current from both the first step-up circuit and the second step-up circuit at the time of the parallel step-up operation; and 
 an electronic control unit configured to control the first and second step-up circuits by generating a first PWM signal for step-up control over the first step-up circuit and a second PWM signal for step-up control over the second step-up circuit, the electronic control unit being configured to, at the time of the parallel step-up operation and when a temperature of the common switching element exceeds a threshold temperature, execute on time change control such that the following condition i) and condition ii) are satisfied, the electronic control unit being configured to change an on time of at least one of the first PWM signal and the second PWM signal in the on time change control, 
 i) a trailing edge of one of the first PWM signal and the second PWM signal and a leading edge of the other one of the first PWM signal and the second PWM signal connect with each other, and 
 ii) the sum of the on time of the first PWM signal and the on time of the second PWM signal in a single PWM control period falls within a range from the single PWM control period to an allowable period obtained by adding a predetermined time to the single PWM control period. 
 
     
     
       2. The electric power conversion system according to  claim 1 , wherein
 the electronic control unit is configured to execute the on time change control such that the following condition iii) is satisfied, 
 iii) the sum of the on time of the first PWM signal and the on time of the second PWM signal in the single PWM control period coincides with the single PWM control period. 
 
     
     
       3. The electric power conversion system according to  claim 1 , wherein
 the electronic control unit is configured to, when the sum of the on time of the first PWM signal and the on time of the second PWM signal in the single PWM control period before execution of the on time change control exceeds the single PWM control period, set the allowable period such that the allowable period is shorter than the sum of the on time of the first PWM signal and the on time of the second PWM signal. 
 
     
     
       4. The electric power conversion system according to  claim 1 , wherein
 the electronic control unit is configured to, when the following condition iv) and condition v) are satisfied, execute the on time change control, 
 iv) the sum of the on time of the first PWM signal and the on time of the second PWM signal in the single PWM control period before execution of the on time change control is shorter than the single PWM control period, and 
 v) a first power loss is smaller than a second power loss, the first power loss is a power loss that arises in the common switching element based on the first PWM signal and the second PWM signal after execution of the on time change control, and the second power loss is a power loss that arises in the common switching element based on the first PWM signal and the second PWM signal before execution of the on time change control. 
 
     
     
       5. The electric power conversion system according to  claim 1 , wherein
 the electronic control unit is configured to, when the following condition vi) is satisfied, execute the on time change control, 
 vi) a first power loss is smaller than a third power loss, the first power loss is a power loss that arises in the common switching element based on the first PWM signal and the second PWM signal after execution of the on time change control, and the third power loss is a power loss that arises in the common switching element at the time when phase shift control for shifting the trailing edge of at least one of the first PWM signal and the second PWM signal to the leading edge of the other one of the first PWM signal and the second PWM signal without extending or shortening the on time of the first PWM signal before execution of the on time change control or the on time of the second PWM signal before execution of the on time change control is executed. 
 
     
     
       6. The electric power conversion system according to  claim 1 , further comprising an inverter configured to convert direct-current power, output from the first step-up circuit and the second step-up circuit, to alternating-current power, wherein
 the electronic control unit is configured to change a conduction ratio in the inverter in response to a change between output voltages of the first step-up circuit and second step-up circuit before execution of the on time change control and output voltages of the first step-up circuit and second step-up circuit after execution of the on time change control. 
 
     
     
       7. The electric power conversion system according to  claim 6 , further comprising a rotary electric machine configured to be supplied with alternating-current power converted by the inverter, wherein
 the electronic control unit is configured to change the conduction ratio in the inverter in response to a change in efficiency of the rotary electric machine commensurate with a change between the output voltages of the first step-up circuit and second step-up circuit before execution of the on time change control and the output voltages of the first step-up circuit and second step-up circuit after execution of the on time change control.